With flourishing advancements in technologies, various information products are developed to satisfy people's different needs. In early days, the majority of displays are cathode ray tube (CRT) displays. However, because of their huge size and power consumption as well as health concern due to radiation exposure for long-term users, CRT displays are replaced gradually by liquid crystal displays (LCDs) at present. LCDs own the advantages of lightness, thinness, shortness, smallness, low radiation, and low power consumption. Thereby, they have become the main stream of the market.
Currently, in order to achieve the characteristics of large size, color, thinness, lightness, and low power consumption of LCDs, high-performance light sources have to be developed. LCDs are non-light-emitting displays. Thereby, in the environment with bad light conditions, illumination methods have to be applied. For example, LCD in a watch utilize a simple light bulb for illumination; those in automotive meters or OA terminals adopt light sources from back of the LCDs for clear displays. The thin and white light sources used this way is named backlight.
A backlight is comprised of a light source and a diffuser. Because the backlight has to be a plane light source, point light sources, such as incandescent lamps, or line light source, such as fluorescent lamps, are transformed to plane light sources via the diffuser. The light sources of traditional backlights include incandescent lamps, light-emitting diodes (LEDs), electro luminescent (EL) lamps, fluorescent lamps, and flat fluorescent lamps. The lighting manners include direct lighting and edge lighting. In general, a LCD panel is composed of a plurality of pixels arranged in matrix form. By inputting image data of each pixel, the brightness of the pixel can be controlled and thus a picture can be displayed on the LCD panel. In addition, because only grey-scale can be displayed for each pixel, another manner has to be utilized to display colors.
LCDs according to the prior art use color filters to display the three primary colors of a pixel and hence colors can be displayed. A pixel of such LCD with color filter is composed of three sub pixels corresponding to red, green, and blue color filters, respectively. Human eyes receive the red, green, and blue lights passing through the color filters and mix them to form the color of the pixel.
Besides, color sequential LCDs according to the prior art display sequentially the three primary colors of a pixel to form color. In this color sequential LCD, each pixel uses three light sources to emit red, green, and blue lights, respectively, as the backlight. In a frame time, the pixel displays three data sequentially corresponding to lighting red, green, and blue lights, respectively. By taking advantage of the visual staying phenomenon of human eyes, people can identify the color of the pixel. In comparison with LCDs with color filters, color sequential LCDs do not need to use color filters and thus costs can be saved. In addition, because only one pixel is needed to determine the color of the pixel in a color sequential LCD, thereby the resolution can be increased by three times.
Nevertheless, the color sequential LCD according to the prior art has several disadvantages. For color sequential twisted nematic (TN) LCDs and color sequential super twisted nematic (STN) LCDs, the control circuit thereof produces a scan signal and a data signal. The voltage difference between the scan signal and the data signal is used to control the orientation of liquid crystals. Hence, the transmittivity of the backlight and thereby the color of output image can be determined. The voltage difference described above is called pixel voltage. Modern scan signal is a voltage signal with a fixed level. The control circuit controls the level of the data signal for adjusting the voltage difference between the scan signal and the data signal to determine the pixel voltage and hence the color of the image. Consequently, when a larger pixel voltage is required for rotating the liquid crystals to larger angles, because the level of the scan signal is fixed, the level of the data signal has to be raised higher. Thus, the power consumption of the control circuit is increased. Furthermore, modern color sequential LCDs have color-mixing problems, which make colors displayed by the displays be deviated from as expected and reduce display performance.
Accordingly, the present invention provides a novel circuit for controlling a color sequential liquid crystal display and a method for controlling the same, which control the voltage difference between the scan signal and the data signal by adjusting the voltage levels of both the scan and the data signals. Thereby, power consumption of the control circuit can reduced and color-mixing problems can be solved.